A drug delivery device with such a housing is known for example from EP 1 920 794 B1. The housing of this known drug delivery device further comprises a window provided in an aperture of the housing. In pen-type injectors, it is advantageous to display the selected dose number which may be dialed on a number sleeve through a transparent lens or window located in the outer housing of the drug delivery device. The lens acts to magnify the selected dose value thus improving readability. It is important to ensure that the window or lens is robustly and reliably secured to the outer housing so that it does not become dislodged, or fall out during use of the drug delivery device. Achieving such a robust connection between a window or lens component and the housing may be a technical challenge.
One known example of achieving this is to form the components together as a two-shot molding. However, this requires an expensive tool and limits the material (usually polymers) and possible printing options for the parts. As an alternative, the window and the housing may be clipped together. However, to ensure that a robust connection is made, a reasonable depth of engagement is required between the parts to accommodate flexible clip features. This arrangement may complicate printing of the window or lens and may increase the overall size of the device. A further option could be to bond the parts together using an adhesive or double-sided tape. However, the use of adhesives and tape requires careful control in the production environment and can have significant cost and complexity implications.